The board position after Black queens with a check and white can play Nf1, Rf1 or Bf1 to save the check.
Anand played Nf1.
The evaluation line was expecting Bf1 and below are some possibilities with a few lines leading to a checkmate in favor of Anand.
If White had played, Bf1
and black responds with Qxf6 because the impending R - > h4 threatens mate on h7 and black has to rescue its king from it
and if intead of Qxf6, if black plays Nxf6 White's gxf6, Qg7# wins for White.
But then if it were only a child's play! :)